(1) Field of the Invention
The present invention relates to non-destructive testing and particularly to a medical diagnostic technique wherein soft body tissue may be serially examined at the same examination site by two different modalities neither of which requires invasion of body or the use of ionizing radiation. More specifically, this invention is directed to apparatus which employs low intensity light and ultrasonic energy to obtain information on the nature of an object being examined and particularly to medical diagnostic apparatus which produces a display commensurate with the amount of absorption at each point in soft tissue under examination of light at different wavelengths and a display commensurate with the ultrasonic energy reflected from the boundaries of regions within the tissue which are characterized by different impedances to passage of ultrasonic energy. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention has particular significance as a breast examination device and method. A recent technological advance in the examination of breast and other soft body tissue consists of transilluminating the tissue with light at a plurality of selected different wavelengths and using digital computation techniques to determine the transmissivity at each selected wavelength of the transilluminating light at each point of the tissue within the viewing field. The computed transmissivity, i.e., the degree of absorption of the light at each transilluminating wavelength, is subsequently employed to create a multi-color image wherein the different colors of the display will be indicative of the nature of the tissue. Examples of such transillumination techniques and apparatus may be seen from U.S. Pat. Nos. 4,467,812 and 4,495,949 and from co-pending application Ser. Nos. 620,271 and 621,194. These patents and pending applications are all assigned to the assignee of the present invention and the disclosures of the pending applications are incorporated herein by reference.
Ultrasonic diagnostic techniques for imaging soft tissue are well-known in the art. As is the case with transillumination, ultrasonic imaging has the advantages that it is a non-invasive technique and does not require ionizing radiation. In ultrasonic imaging a fraction of the energy produced by a transducer is reflected when the transmitted energy encounters a change in the characteristic impedance to the passage of ultrasonic energy. The characteristic impedance of the tissue may be defined as a product of the density of the tissue multiplied by the velocity of sound. The energy reflected from the boundaries between regions having different characteristic impedance may be computer processed and a display produced which provides valuable information to the diagnostician. Examples of prior ultrasonic diagnostic systems may be seen from U.S. Pat. Nos. 4,137,777, 4,207,772 and 4,242,911.
Each of the available imaging modalities which is non-invasive and does not employ ionizing radiation, i.e., transillumination and ultrasonic imaging, has advantages and limitations. Thus, transillumination has the ability of providing a "global" view, wherein abnormal areas may be seen, in a relatively short time. A trained technician employing the transillumination techniques and apparatus of the above-referenced patents and applications can detect very small, i.e., non-palpable, lesions. Transillumination cannot, however, provide information as to the depth within the tissue, i.e., the precise location, of an abnormality since the information containing display is essentially produced from shadows which appear at the surface of the tissue being examined. Also, it is not always possible to differentiate between cystic and solid lesions when applying the transillumination modality. Ultrasonic imaging techniques, on the other hand, are not well-suited for survey or global-type studies because the modality, by its very nature, gives a plane of information. Accordingly, in order to obtain the same information using ultrasound as can be obtained through use of transillumination; information would have to be collected in more than one hundred planes. This, of course, would be much too time consuming to be practical. Ultrasound does, however, have the unique ability to precisely locate abnormalities, and particularly lesions, once they have been detected by some other modality. Ultrasound also has the ability to differentiate between cystic and solid lesions with a very high degree of accuracy. Further, when two lesions are located in very close proximity to each other, a well-focused beam of ultrasonic energy will provide information which enables both lesions to be detected and classified.
It would, of course, be possible to serially examine a patient first employing the transillumination modality and then, if the results of the initial examination indicated it to be necessary or desirable, to re-examine using the ultrasound modality. In the past, the available apparatus which employed the transillumination and ultrasound modalities were "stand-alone" type equipment which, while available in a well-equipped radiology department, would be at different examination sites and would be unable to communicate with one another. Thus, the inconvenience of moving the patient from one examination site to another had to be accepted. Perhaps of more significance, it was extremely difficult to provide the radiologist simultaneously with the results of the transillumination and ultrasound techniques so that a side-by-side comparison could be made. The latter problem was aggravated by the different degrees of resolution of the apparatus for implementing the two modalities and by the different rates at which data is collected during the use of the two modalities.